Centrifugal casting is a common method used for casting tubular metal articles including engine cylinder liners. The centrifugal casting apparatus is typically a cylindrical shaped metal mold that is rotated about the longitudinal axis at sufficient speed to distribute the molten metal along the inner surface of the mold. The molds are generally made of metal and have the inner mold surface covered with a lining material to protect the mold from damage and overheating by contact with molten metal. The lining material also is provided to prevent the molded article from bonding to the mold surface.
One method for applying a lining to centrifugal casting molds applies a slurry of a fine particulate refractory material. The refractory materials are typically zircon powder or silica powder and a binder such as bentonite clay. Applying a slurry of a refractory material to a mold surface has exhibited some success. However, a disadvantage of this method is that the mold requires adequate venting to vent water vapor produced during the casting process.
Other methods of forming a mold lining use a binder material, such as a resin, to bond the particles together and to bond the material to the surface of the mold. These methods can be difficult to apply and form a uniform surface. In addition, the application of a lining material using a binder can be expensive and produce gaseous products by the heat from the molten metal during the casting of the metal article.
The vast majority of centrifugal castings employ horizontal casting. For example, the water pipe industry made of iron in thickness of ¼″ to 1″ in diameter of 2″ to 64″ in weights up to 11,510 lbs. in lengths of 18 and 20 feet.
American Centrifugal cast steel tubes in lengths of 20 feet and diameters of 30 inches with wall thickness up to 7 inches, in weights up to 28,800 pounds. Therefore, centrifugal casting is not limited to diameter, length or wall thickness and is geared to much faster production rate and higher yield of 95% compared to the 35% that static casting achieved in the 500-pound ductile iron bomb body program.
However, centrifugally casting horizontally has a serious disadvantage when the article requires a thick heavy wall such as the bomb body. The revolving mold wall will pick up ½ inch of liquid metal rapidly being cast onto the relatively cold surface of the mold. Casting a thick heavy wall article requires a much longer pouring time because the additional metal does not receive the chilling effect of the mold or the friction of the mold wall. Metal that does not receive sufficient speed from friction to overcome the effects of gravity will fall back as rain thus aerating the metal and causing oxidation. Therefore, multiple pours of ½ inch metal thickness or less are required. However, the intermittent cooling between pours by the convection air current causes the inside surface of the metal to solidify before the mid wall section, causing internal porosity shrinkage.
The oxidation of the metal is detrimental to all molten metals during casting. Therefore, there is a need for an improved method for pouring the horizontal centrifugal casting method of thick wall constant bore tubular articles.
Previous U.S. Pat. Nos. Re 17,220, dated Feb. 19, 1929, original U.S. Pat. No. 1,533,780 to Robert F. Wood and U.S. Pat. No. 2,344,020, dated Mar. 14, 1944 to Jacques Boucher relate to producing a centrifugally cast metal tube closed on one end with a tapered bore and closed on both ends by pouring the spinning mold while in an inclined position. Pouring an inclined mold is similar to pouring the mold in the horizontal position where pouring is limited to small quantities of molten metal to prevent the metal from falling back (raining) and oxidizing.